In the past, technique for detecting the pupil of a subject has been known. This technique is applicable to detection of a see-through driving, detection of drowsiness of a driver, investigation of the degree of interest of a product, data input to a computer, and the like.
With respect to such pupil detection technique, the following Patent Document 1 discloses a pupil detection method of detecting a pupil by acquiring a bright pupil image, an unilluminated image, and a dark pupil image and then performing image difference processing thereon. In this method, a corneal reflection image is detected from a difference image acquired by subtracting the unilluminated image from the bright pupil image or a difference image acquired by subtracting the unilluminated image from the dark pupil image. In these difference images, since only images by respective light sources are acquired, the corneal reflection can be easily detected by removing an image of ambient light (disturbance light) such as the sun. Therefore, the pupil can be detected by performing position correction based on corneal reflection with respect to the two difference images and subtracting the difference images from each other.